Chapter 0 : Introduction to Object Oriented Design.

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Chapter 0 Introduction to Object Oriented
Design.
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The science of computing
computer science is a science of abstraction
creating the right model for a problem and
devising the appropriate mechanizable techniques
to solve it. A. Aho and J. Ullman
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Nature of a software system

• A software system is a temporary solution to a
  changing problem.
• With two fundamental characteristics
• they are dynamic
• they are complex.

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Dealing with complexity composition and
abstraction

• Size of software system
• must be broken down into manageable pieces
• Must be dealt with as a composite structure.
• Parts must interact together.
• The more parts the more interaction.
• System complexity is proportional to the number
  of parts.

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Dealing with complexity composition and
abstraction

• composition
• process of building a system using simpler parts
  or components

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Dealing with complexity composition and
abstraction

• Abstraction can deal with system components with
  no worry about details of how components are
  constructed.
• abstraction
• process of ignoring details irrelevant to problem
  at hand
• Emphasizes essential ones.
• To abstract is to disregard certain
  differentiating details.

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Two aspects of a system data and
functionality

• data information program deals with
• data descriptions are fixed,
• individual data values change each time program
  runs

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Two aspects of a system data and
functionality

• functionality what the program does with data.
• computation a goal-directed sequence of actions
  performed by a processor.
• algorithm ordered set of instructions describing
  pattern of behavior guaranteed to achieve some
  goal.

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Software Systems View
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Object-oriented systems

• Use the Object Oriented approach for structuring
  systems.
• Intended to produce systems that are
• modular
• composite
• built using abstraction
• organized around data

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Object-oriented systems

• Objects abstractions used to decompose the
  problem.
• System Functionality distributed among objects.
• Each object has
• properties to represent the data it manipulates
• algorithms to accomplish specific tasks.